1. Field of the Invention
The present invention relates to a flash control system for remotely controlling a flash-light emission of an external flash device by a light signal output from a camera associated with the external flash device.
2. Description of the Related Art
Conventionally, a flash-light emission of an external flash device is remotely controlled by a camera in accordance with a so-called slave method. Namely, when a flash light is emitted from a built-in flash device of the camera, the emitted flash light serves as a trigger for initiating an flash-light emission of the external flash device.
In this external flash control system, an amount of the flash-light emission of the external flash device cannot be accurately controlled, because only a timing of the flash-light emission of the external flash device is adjusted, with the amount of the flash-light emission being fixed. Thus, it is difficult to provide highly accurate exposure in response to photographing conditions which are variable depending on an object-distance or the like.
Therefore, an object of the present invention is to provide a flash control system for remotely controlling a flash-light emission of an external flash device by a light signal output from a camera, in which both a timing and an amount of the flash-light emission are properly and accurately controllable.
In accordance with an aspect of the present invention, there is provided a flash control system for remotely controlling an external flash device by a camera associated with the external flash device. In the flash control system, the camera includes a stop value calculator that calculates a stop value as an exposure factor for the external flash device, a light signal source that emits a light signal, and a light signal controller that controls the light signal source to emit at least two light signals therefrom at a time interval such that the stop value is represented by the time interval between the two light signals. The external flash device includes a light signal detector that detects the two light signals emitted from the light signal source, and a flash-light emission controller that controls an amount of the flash-light emission of the external flash device in accordance with the time interval between the two light signals.
Preferably, in the flash control system, the camera further includes a flash-light emission timing calculator that calculates a flash-light emission timing at which a flash-light should be emitted from the external flash device. In this case, the light signal controller further controls an emission of one of the two light signals such that the flash-light emission timing is represented by the emission of the one of the two light signals, and the flash-light emission controller further controls a timing of the flash-light emission of the external flash device in accordance with the emission of the one of the two light signals. Preferably, the control of the timing of the flash-light emission of the external flash device by the flash-light emission controller is based on a last light signal of the two light signals.
The calculation of the stop value by the stop value calculator may be based on at least a photometry measurement performed by the camera upon photographing. Also, the light signal source may comprise a flash lamp of a built-in flash device incorporated in the camera.
Preferably, the flash-light emission controller includes a light detector that detects the flash-light emission of the external flash device as a reflected light, a first processor that processes the reflected light, detected by the light detector, to produce a first light-quantitative data representing an amount of the reflected light, a second processor that processes the time interval to produce a second light-quantitative data deriving from the stop value, and a comparator that compares the first light-quantitative data with the second light-quantitative data, such that the flash-light emission of the external flash device is stopped when it is determined by the comparator that the first-quantitative data coincides with the second light-quantitative data. The light detector may comprise the light signal detector for detecting the two light signals.
In accordance with another aspect of the present invention, there is provided an external flash device, which comprises a flash lamp that emits a flash-light, a light signal detector that detects two light signals emitted at a time interval rep-resenting a stop value as a photographic exposure factor, and a flash-light emission controller that controls an amount of a flash-light emission of the flash lamp in accordance with the time interval between the two light signals.
Preferably, the external flash device further comprises a timing controller that controls a timing of the flash-light emission of the flash lamp on the basis of a detected-timing at which one of the two light signals is detected by the light signal detector. Preferably, the control of the timing of the flash-light emission of the flash lamp by the flash-light emission controller is based on a last light signal of the at least two light signals.
Preferably, the flash-light emission controller includes a light detector that detects the flash-light emission of the external flash device as a reflected light, a first processor that processes the reflected light, detected by the light detector, to produce a first light-quantitative data representing an amount of the reflected light, a second processor that processes the time interval to produce a second light-quantitative data deriving from the stop value, and a comparator that compares the first light-quantitative data with the second light-quantitative data, such that the flash-light emission of the flash lamp is stopped when it is determined by the comparator that the first-quantitative data coincides with the second light-quantitative data. The light detector may comprise the light signal detector for detecting the at least two light signals.
In accordance with yet another aspect of the present invention, there is provided a camera, which comprises a stop value calculator that calculates a stop value as a photographic exposure factor for an external flash device, a light signal source that emits a light signal to the external flash device; and a light signal controller that controls the light signal source to emit at least two light signals therefrom at a time interval such that the stop value is represented by the time interval between the at least two light signals.
Preferably, the camera further comprises a flash-light emission timing calculator that calculates a flash-light emission timing at which a flash-light should be emitted from the external flash device. In this case, the light signal controller further controls the emission of the at least two light signals such that the flash-light emission timing is represented by an emission of one of the at least two light signals. Preferably, the control of the emission of the at least two light signals by the light signal controller is performed such that the flash-light emission timing is represented by an emission of a last light signal of the at least two light signals.
When the camera comprises a lens shutter type camera, a timing of the emission of the last light signal of the at least two light signals coincides with a time at which an aperture of a shutter of the lens shutter type camera reaches a maximum aperture during an opening-action of the shutter.
When the camera comprises a single lens reflex type camera, a timing of an emission of a first light signal of the at least two light signals coincides with a time, at which a leading shutter curtain of a focal-plane shutter of the single lens reflex type camera reaches an end position thereof.